This invention relates generally to the emission of vaporized material from a source in a high vacuum (HV) environment and relates, more particularly, to the means and methods for controlling the flux and other emission parameters attending the vaporized material.
Material which has been vaporized from a source is used in many growth/deposition applications wherein atoms and/or molecules of the vapor are deposited upon a substrate in a HV environment. Such applications include molecular beam epitaxy (MBE), electron-beam epitaxy, sputtering, laser ablation, thermal evaporation and metal organic chemical vapor deposition (MOCVD). In each application, the material is emitted from a source in a vapor and directed toward the surface of a substrate for deposition thereon. In an MBE process, for example, material to be vaporized is contained within an effusion cell and vaporized from the cell by appropriate heating means.
One parameter, or characteristic, attending the emission of vaporized material from the source is the flux of the material. The flux of the vaporized material is the rate of discharge of the vaporized material from the source (measured, for example, in atoms per second per centimeter squared) and has heretofore been controlled in deposition applications by controlling the temperature of the source. Generally, therefore, in order to increase the flux of vaporized material from the source, the source material is heated to a higher temperature, and in order to decrease the flux, the temperature of the source is lowered. Such an approach possesses disadvantages, however, which can relate to irreproducible fluxes, long equilibration times, and delays in growth necessary to measure and adjust the flux. Thus, prior art methods for controlling flux solely by temperature-control schemes are time-consuming in nature.
On the other hand, the control of the flow or emission of the vaporized material from the source, rather than the flux, commonly involves the use of a mechanical shutter which is mounted for pivotal movement adjacent the mouth of the source. During a deposition process involving such a shutter, the shutter is pivotally moved back and forth across the mouth of the source between two positions (i.e. opened and closed positions) to control the exposure of the substrate to the source and consequently control the flow of atoms and/or molecules from the source toward the substrate.
If such mechanical shutters are operated rapidly (to provide, for example, an open period of no more than 1.6 seconds), the uniformity (i.e. flatness) of the flux profile emitted from the source suffers, and the uniformity of the resulting deposition suffers accordingly. Therefore, to ensure that the flux profile is relatively uniform, the periods of time that these shutters are open are typically no less than 1.6 seconds in duration. Consequently, a deposition process performed with such shutters is a time-consuming process, and when considering the fact that temperature-control schemes are time-consuming in nature, as mentioned above, some prior art vapor deposition processes performed in a HV environment have not heretofore been considered to be practical for mass production processes. In other words, the time-related constraints which attend prior art vapor deposition processes of this class (such as MBE) have so far outweighed the benefits gained by such prior art deposition processes that these processes have not heretofore been employed in silicon-based semiconductor fabrication facilities.
It is an object of the present invention to provide a new and improved shutter apparatus and system for controlling parameters attending the emission of vaporized material from a source in a growth/deposition application involving a HV environment and an associated method.
Another object of the present invention is to provide such an apparatus and system capable of controlling the flux and related parameters of the vaporized material with a high degree of accuracy and which circumvents many of the time-related constraints attending vapor deposition processes of the prior art.
Still another object of the present invention is to provide such an apparatus and system enabling the growth of stoichiometric line compounds with greater accuracy and control over the growth process, and which promotes uniformity of growth of the deposited materials upon a substrate and a more rapid deposition of vaporized material than was capable of being achieved with conventional deposition processes.
Yet another object of the present invention is to provide such an apparatus and system wherein the parameters attending the vaporized material can be adjusted so rapidly while preserving the uniformity of the flux profile that vapor deposition processes of the prior art which have heretofore not been considered as practical for mass production processes are now practical.
A further object of the present invention is to provide such an apparatus and system which is uncomplicated in construction yet effective in operation.